Einstein's War

by Matthew Stanley

ORIGINAL ILLUSTRATION BY JACOB FORD

  One of the tasks of the Royal Observatory was to study solar eclipses. Total eclipses allowed astronomers to see phenomena otherwise impossible to observe, such as the corona or solar prominences. While the time and location of eclipses could be predicted with great accuracy, they rarely happened in a convenient way. Rather, the path of totality might be over ocean or other inaccessible areas. Astronomers wanting to view the eclipse would have to mount elaborate and expensive expeditions to be in the right place at the right time. Months of planning and travel might still result in a cloudy day that produced nothing.

  Eclipse expeditions became more feasible in the late nineteenth century as imperialism made it easier and easier for Europeans to access far-flung regions such as the African interior. Naval bases and growing railway networks allowed astronomers to penetrate into areas formerly completely impassable. These expeditions relied on the infrastructure of empire, but as historian Alex Soojung-Kim Pang has shown, they were themselves demonstrations of imperial strength. A British expedition to view an eclipse in India, say, was a show of power over colonial subjects. They were government-funded symbols of superiority, sophistication, and money to spare. Even countries without extensive colonial possessions would often organize expeditions as a way of demonstrating “scientific maturity and vigor.”

  Such expeditions were physically grueling and time consuming, and the Astronomer Royal almost always sent the chief assistant into the field in his place. When Dyson was the assistant he was a famously lucky observer of solar eclipses, with good weather six out of six times. Now that he was in charge, though, the task of observing the 1912 eclipse was delegated to Eddington. British eclipse projects were organized by the Joint Permanent Eclipse Committee (JPEC) of the Royal Society and Royal Astronomical Society since 1894. JPEC secured government grants, organized personnel, and curated the necessary equipment. Dyson and the JPEC decided that the 1912 eclipse would be best observed from Brazil. Eddington was given the travel details and put in charge of two assistants, Charles Davidson and J. J. Atkinson—generally operating the photographic equipment for an eclipse required three skilled workers. He packed Darwin’s Voyage of the Beagle to read on the ship and departed Southampton on August 30. Eddington had some experience with preparing and shipping equipment from his time on Malta but there was constant worry that the delicate instruments would be damaged by rough-handed stevedores. This trip had the additional concern of dealing with customs officials, who were often confused by and suspicious of elaborate scientific tools.

  The Royal Mail Steam Packet Company carried the group and their equipment free of charge. Their ship passed through Lisbon, which Eddington was delighted to explore. He wrote to his mother about visiting a cathedral where he saw a “mummy of a tiny girl saint.” The group landed in Rio on September 16. The Brazilian interior was accessible thanks to new railroads laid down to supply the huge numbers of new plantations that had been springing up. The trains were intended to carry cotton, coffee, and beef, but they handled astronomers and telescopes just as well. The Brazilian government provided them free passage.

  It took about six days to get to Passa Quatro, a village about 180 miles from Rio. Keeping track of all their equipment and luggage was hard—at one point Eddington had to sleep on the train platform to make sure they didn’t miss their train. The observing site (marked ahead of time by Brazilian astronomers) was a mile from the railway, and the equipment was brought in by oxcart. Local workmen built a brick foundation to support the heavy gear. Three waterproof canvas huts had been brought from Greenwich. The telescopes and spectrograph were set up horizontally in the huts. A clockwork-driven mirror called a coelostat was placed in front of them, reflecting the image of the sun down through the lenses to the photographic plates (see page 58). The sun would move appreciably across the sky during the eclipse, so the coelostat was needed to keep the image steady for the photograph. One of the huts was made light-tight and arranged for developing the photographs. It took nearly two weeks to set everything up, during which the Englishmen complained about the greasy food and the unacceptable tea.

  The astronomers had planned an elaborate series of photographs to be taken with four instruments over the few minutes of the eclipse. This would require a finely orchestrated sequence of events executed with military precision: glass plates were slid out of wooden boxes, placed exactly so in the telescope, exposed, removed, and placed into black canvas bags, all while the clocks ticked and the moon crossed the face of the sun. These actions were rehearsed over and over for three days straight until the group was a finely honed machine. One of the coelostats gave Eddington quite a bit of trouble. Its intended smooth turns kept skipping and halting. Eventually they got everything working properly, only to realize that the Brazilians had made a longitude error and the site was some seven miles off the path of totality. But it was too late to move, and a partial eclipse was still valuable.

  An eclipse observation set up in the field. The telescopes lie horizontal under the protective hut. The coelostat mirror can be seen to the left.

  SCIENCE AND SOCIETY PICTURE LIBRARY

  Crushingly, heavy rain set in the day before the eclipse and continued for a week. The highly disciplined observers waited by the instruments even as they saw nothing but cloud, watching for just a moment of clear sky. There was a sudden onset of darkness at the moment of the eclipse but the sun could not be seen. There was intense disappointment, as the expedition proved entirely unsuccessful after months of planning. Despite the rain, the president and foreign minister of Brazil, as well as several ambassadors, arrived with bands and fireworks. There was a banquet afterward with many speeches in Portuguese, of which Eddington understood not a word.

  While a scientific disaster, the trip had other benefits. Eddington was able to get to know Charles Dillon Perrine, an expat American who had been appointed director of the Argentine National Observatory. Like Greenwich, that institution had planned to make several different observations during the eclipse. Most of them would be photographs and spectrographs of the corona, but Perrine also wanted to carry out a test requested by an acquaintance in Berlin—Erwin Freundlich. This was to check a recent prediction that the sun’s gravity could bend starlight, displacing stellar images. Eddington surely chatted with Perrine about the project. Perrine would have explained that the prediction had come from a German physicist named Einstein—likely the first time Eddington had heard the name. It sounded like an interesting idea, although not really in Eddington’s area of research. And since the observation had failed due to the weather, there wasn’t much reason to look more closely at it. Eddington filed it away in the back of his memory.

  Brazil had other benefits too. Eddington decided to indulge his glissading obsession and tobogganed some three thousand feet down a mountain. It took about half an hour. He explored the forest on horseback, was charmed by the flying fish in the bay, and watched a battle between two armies of ants. Even more wondrous was seeing fireflies in the rain during a lightning storm: “The scene was like fairyland.” All of his local companions gave him the Brazilian farewell ritual, described by Eddington as a hug followed by three pats on the back. The British team sailed for home on October 23 on the Danube.

  The next April, Eddington and Trimble had their usual Easter walking tour together. They agreed it was one of their best trips despite constant rain. While on that holiday he received some extraordinary news. He had been offered an appointment as Plumian Professor of Astronomy and Experimental Philosophy at the University of Cambridge. This was one of the most distinguished positions in astronomy in the entire country—it dated back to 1704, when its original statutes were drawn up by Isaac Newton. Along with the professorship came the directorship of the Cambridge Observatory. Eddington’s time at the Royal Observatory had marked him as one of the leaders in the British scientific community, and this position made that official. He cut short his holi
day with Trimble to begin handling the not-insignificant paperwork.

  Eddington stayed in London through July, when he moved back to Cambridge. He was delighted to rejoin the Quaker community from his student years. The humble Meeting House on Jesus Lane was unchanged. He was known as an unostentatious worshipper there and refused the honor of sitting in the front of the hall that his status as a professor would have allowed him. For the rest of his life he served on various committees for the Friends and, as a skilled mathematician, handled their accounts.

  Without academic responsibilities for the rest of the summer, Eddington went to Bonn for the Solar Union conference and afterward to Hamburg for the meeting of the Astronomische Gesellschaft (the German equivalent of the Royal Astronomical Society). He got to know Karl Schwarzschild quite well on that trip, taking a ten-mile hike with him to Drachenfels Castle. They posed with Dyson and some other friends for a comic photograph with a wooden donkey, a fine composition Eddington titled “Schwarzschild & five mad Englishmen.” On his way home he stayed with the family of the astronomer Ejnar Hertzsprung in Copenhagen. He was congratulated widely on his new position and came back to Cambridge exhilarated after a month of intense intellectual engagement.

  Upon his return he had to stay in temporary rooms. The Cambridge Observatory had living quarters for the director in the east wing so they would never be far from their work, but he was unable to move in promptly. The observatory directorship was technically a separate position from the Plumian professorship and there was some bureaucratic wrangling before he was able to officially take over. Eddington moved in on March 25, 1914. Cambridge was now his home, though he was regularly in London for scientific meetings and to talk with colleagues.

  Typically the director of the Cambridge Observatory would have been married and his wife expected to run the household and act as hostess for scientific dignitaries. The unmarried Eddington brought his sister, Winifred, to live with him and take on those duties. She filled that role for his entire life. As his biographer Alice Vibert Douglas stated, “His interest in women was simply and solely as acquaintances or, in the case of the very few women astronomers in various countries, as friendly colleagues.” The Eddingtons brought with them Monty, a cat, and Punch, an Aberdeen terrier “not universally beloved.”

  The observatory sat behind a modest classical façade about a mile west of the university. Upon entering the building, one turned right into the library. Through a door from there was Eddington’s study, the only untidy space in an otherwise fastidious home. Piles of scientific papers on the floor and couch; bookshelves stuffed with both astrophysics and P. G. Wodehouse novels. He would meet with students there, perusing calculations while petting his terrier. Eddington loved the observatory’s garden and nearby woods. Visitors were inevitably taken along the walkway and shown Miss Eddington’s beehives.

  As Eddington settled into his tranquil surroundings in Cambridge, Britain as a whole was more uncertain. The nation had been dealing with episodes of industrial unrest, including a 1911 dock strike and one in coal country the following year. Geopolitical tension had increased steadily if sporadically. Fear of growing German power was quite real, and the Daily Mail even ran a series describing a fictionalized Prussian invasion in great detail. Erskine Childers’s Riddle of the Sands was a bestselling thriller about an imminent German attack. The arms race had a brief respite after diplomatic interventions in 1912, and the kaiser decided that his attention was better spent on the army than the navy (Britain’s only real concern).

  More likely than a direct confrontation with Germany was Britain being pulled into a difficult situation by their allies France and Russia. Those three countries had formed the Triple Entente in 1907—a loose group intended to counterweight the Triple Alliance of Germany, Austria-Hungary, and Italy. The Entente was a general understanding rather than a formal mutual-defense agreement, so each country was free to make its own foreign policy. The inclusion of despotic Russia with Europe’s two great democracies made many uncomfortable.

  The division of Europe into these two power blocs was precarious. It was not always certain who was making decisions about foreign relations—Kings? Ministers? Legislatures? When Kaiser Wilhelm threatened the king of Belgium at a dinner party, was that an official statement of policy or merely a drunken monarch known for erratic behavior? Nonetheless the system had already survived various crises; imperial clashes in Africa were generally handled with some level of diplomatic skill. Everyone was fairly cautious. The two alliances were closely matched in military terms, and it was not clear who would prevail in a conflict.

  The persistent area of tension between the blocs was the Balkans. Austria-Hungary had been occupying Bosnia and Herzegovina since 1878 and formally annexed them in 1908. Those regions had large populations of Eastern Orthodox Christians isolated by centuries of sequential invasions. The Russians saw themselves as the traditional protectors of those populations and were not at all happy about the Austrian control there. Independence movements spurred by Serbia kept the situation fluid and sabers were rattled constantly. Arguments between Russia and Austria became heated in November 1912, but diplomats were again able to calm the situation.

  In a show of imperial control over the region, Archduke Franz Ferdinand, the Austrian heir, planned to visit Sarajevo in the summer of 1914. This seemed a perfect opportunity for a group of Serbian nationalists known as the Black Hand to deal a blow against their oppressors. Three nineteen-year-old men from unhappy households were recruited and given four revolvers and six bombs. As they were smuggled across the border, their drunken escort bragged, “Do you know who these people are? They’re going to Sarajevo to throw bombs and kill the Archduke who is going to come there.” The sickliest of the group, Gavrilo Princip, nodded and confidently brandished his revolver. He was an excellent shot.

  CHAPTER 3

  The Wars Begin

  “A sin against civilization.”

  THROUGHOUT HIS LIFE people asked Einstein not just about what his science meant but also about how he did his science. How did he create the theory of relativity? An often-quoted answer was his claim that doing theoretical physics was merely finding the “simplest conceivable mathematical ideas” and then checking them against experience. “In a certain sense, therefore, I hold it true that pure thought can grasp reality, as the ancients dreamed.” This is the image we often have of Einstein—a genius of ultimate rationality, sitting at his desk and smoothly deducing the nature of the universe.

  Einstein also warned us, though, not to believe him. In a candid moment he admitted, “If you want to find out anything from the theoretical physicists about the methods they use, I advise you to stick closely to one principle: do not listen to their words, fix your attention on their deeds.” Taking his advice, we will follow Einstein down the complicated road he took toward his general theory of relativity. Far from being a serene journey of pure thought, the road wandered from battle to battle. Einstein had to fight through struggles of all kinds—mathematical, conceptual, personal, and, eventually, war.

  BY THE TIME Einstein was able to bring his focus back to relativity and gravitation he had a lot of catching up to do. Minkowski’s reframing of special relativity had attracted a fair bit of attention. Henri Poincaré extended it further, and that pair provided a mathematical foundation for others to explore relativity. Planck’s assistant Max von Laue actually wrote the first textbook on relativity in 1911 using Minkowski’s, rather than Einstein’s, presentation.

  Two other physicists, Max Abraham and Gunnar Nordström, also used Minkowski’s format to follow up on Einstein’s brief 1907 suggestion that relativity might be connected to gravity. They were not the first to propose alternatives to Newton’s theory. There were a few options proposed around the turn of the twentieth century, usually trying to explain gravity as a special case of electromagnetism. And electromagnetism at the time meant ether theory—Lorentz commented that ether theory ha
d been so successful with electricity and magnetism that it was “natural” to also use it to understand other forces.

  In 1911, Max Abraham, a theorist at the University of Göttingen and former student of Max Planck, started work on his relativistic theory of gravity. Although his theory explicitly built on the equivalence principle, Einstein was generally unhappy with it. It allowed the speed of light to vary and thus broke with the basic postulates of special relativity. It also stuck closely to Minkowski’s version, which Einstein thought was mathematically impressive but lacking in physical insight—that is, it told us little about what was happening to real objects in the material world. He also complained that Abraham provided few ways to check his theory observationally. In particular, Abraham did not predict the gravitational bending of light.

  Einstein and Abraham fired letters back and forth about these critiques, and their dispute became public in 1912. Einstein saw Abraham’s theory as endangering the very foundations of relativity. Abraham’s reliance on mathematical elegance as a guide had, Einstein thought, led him astray. “That’s what happens when one operates formally, without thinking physically!” He dismissed the theory as “a stately beast that lacks three legs.”

  The Finnish physicist Gunnar Nordström watched their clash from afar before he presented his own theory. Nordström tried to keep his theory as close to Newton as possible, adopting only the essentials from special relativity. He kept the speed of light constant but did not predict either the anomalous motion of Mercury or the deflection of light. Otherwise, though, his theory was robust and fulfilled most of what someone might have wanted from a Newton alternative at the time.

  With competition from Abraham and Nordström, Einstein had to produce something soon. He had been pondering “ceaselessly” on gravity for three years but published nothing. Reluctant to take up Minkowski’s mathematical route, he was still trying to understand the physical meaning of his own equivalence principle. What exactly did it mean to say that acceleration and gravity were equivalent? His initial thought experiments involved linear acceleration—that is, being pushed in one direction only. But he started thinking about one special case of acceleration—rotation. Acceleration is any change in the amount or direction of your speed, and if you are spun around in a circle the direction of your travel is constantly changing. So rotation or spinning is considered to be continuous acceleration.